Home of Professional Cinematography since 1996

RED Stainless Mount

Published : 1st May 2010

Can't remember if the RED backfocus drift and aluminium mount controversy was here, but I was just glancing through the Element Technica catalogue and read (p.21):

"The Panavision Stainless Lens Mount is sleek, ergonomic, and RED approved. This high-quality stainless mount is easily installed and its thermal stability helps back focus stay constant."

So there you have it from a trusted source. RED absolutely approves of third party stainless replacement mounts promising improved thermal stability.

At least as long as one is shooting PV glass

Tim Sassoon
SFD
Santa Monica, CA


We made one (stainless mount PL mount) and have approved Element Technica's PV mount. While everyone seemed to talk about the problem... no one we know ever seemed to have a real problem (other than not tightening down the bolts well).

We can certainly sell you one if you want. Just make sure you need it instead of listening to others speculate that it must be an issue. We love to sell stuff. But I sure can't say that you need it. Steve Meizler commented that he checked the back focus every day on 4 movies and it was never off once. That included shooting in wicked temps (Ché in Spain and Bolivia), heavy humidity (Ché in Puerto Rico), and cold (The Informant!).

EPIC and Scarlet mounts are completely different. The adjustment is a 5 axis lock down mechanism that is internal to the body. While the actual lens mounts are aircraft aluminium, they are certainly capable of being swapped out for any material you want. They are very simple in design so it won't cost much if you feel the need.

We believe one thing, but are certainly open to another's opinion and are designing everything so you can do just about anything you want to change to your way of thinking.

Jim Jannard
www.red.com
WA, NV & CA


It is interesting to note that Russian 35mm cine cameras like the Kinor 35H were made with Magnesium alloy bodies but had a carbon steel chassis. The coefficient of linear thermal expansion (without units) for carbon steels are around 10, common stainless steels are around 17, while Aluminium alloys are in the low 20s. Should the sensor/lens mount chassis be made of a carbon steel? I don't know...

Maybe Jim is right. Does the material matter in this design...?

Cya


Steve

Scientific Imaging
Monash University
Melbourne
Australia


>> Steve Meizler commented that he checked the back focus every day on 4 movies and it was never >>off once. That included shooting in wicked temps (Ché in Spain and Bolivia), heavy humidity (Ché >>in Puerto Rico), and cold (The Informant!).

Then I'm not sure why we had to reset the back focus on a RED ONE twice in one day during summer in San Francisco.

-----------------------

Art Adams | Director of Photography
4 1 5 . 7 6 0 . 5 1 6 7

showreel -> www.artadams.net
trade writing -> art.provideocoalition.com

ICG, SOC, NWU


Art :

>>"Then I'm not sure why we had to reset the back focus...."

Probably because the mount was not properly set and tightened in the first place. I've had my camera for a year and although my assistants check back focus before every job it has not needed any adjustment whatsoever.

Florian Stadler, D.P., LA
www.florianstadler.com


>>Probably because the mount was not properly set and tightened in the first place.

No, it was definitely heat related. We were fine in the morning, and then when we went outside around midday and the camera heated up we lost back focus within about a half hour. Then, in the afternoon when we spent the rest of the shoot in the shade of a building, it went back to the original setting.

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Art Adams | Director of Photography
4 1 5 . 7 6 0 . 5 1 6 7

ICG, SOC, NWU


Art...

If the mount is not tightened properly, it will shift with heat. Every time someone has complained about this (maybe 3 times), we have gone on set and found the mount not tight. If you don't believe me... you can always buy the stainless steel mount.

Jim Jannard
WA, NV & CA


>> Probably because the mount was not properly set and tightened in the first place.
>> No, it was definitely heat related.

Not mutually exclusive...

There are two sets of cap screws involved in holding the mount assy to the camera body...if they are not all torqued correctly, they can allow for movement as the camera heats up and cools down as separate from the dimensional change of the aluminium mount itself.

the way most screws work is that when tightened, they actually deform (they elongate or stretch)
It is the springiness of that stretch that holds things together when you bolt them together and the bolt is in tension(as opposed to what happens when you use screws or bolts as pins and
they are loaded in shear)

If the some screws are tighter than others (if some springs are stronger than others) things can move in relation to each other as things heat and cool.

Mark H. Weingartner
LA-based VFX DP/Supervisor

http://schneiderentertainment.com/dirphoto.htm


>> Art... if the mount is not tightened properly, it will shift with heat. Every time someone has >>complained about this (maybe 3 times), we have gone on set and found the mount not tight. If >>you don't believe me... you can always buy the stainless steel mount.

Screws expanding and contracting are a new one on me. Just when I think I've finished my doctoral studies in cinematography someone always throws in a new class requirement.

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Art Adams | Director of Photography
4 1 5 . 7 6 0 . 5 1 6 7

ICG, SOC, NWU


Exactly.

A classic example of this are the TTY (Torque To Yield) head bolts used on many cars these days. You actually torque these to a given spec and then turn them a given number of degrees past this point. This stretches the bolts a predetermined amount to maintain constant pressure under temperature changes. Of course, you don't reuse these bolts, you discard them and use new ones.

Aluminium actually does not have a CE that much different that stainless steel - about 15 percent greater - so it would not make that much difference in back focus drift with temperature. Stainless's main advantage is that it is harder and thus stands up to wear and tear better. Tightening a lens mount to the correct torque and cross tightening as you go to equalize stress (like wheel lugs) will usually eliminate any problems. This applies to many other camera besides just the Red...

Tom
Torqued Off in L.A.


>> We can certainly sell you one if you want. Just make sure you need it instead of listening to >>others speculate that it must be an issue. We love to sell stuff. But I sure can't say that you need >>it.

Jim,

The problem does not surface under what you would consider normal operating conditions, hot, cold or otherwise. It was however an issue when there was a wide temp variance throughout the day. By wide I mean 20C+. So for 95% or more this is unlikely to be a problem.

10C was tolerable, but we were seeing upwards of 25-30C shift over a few hours. By late morning you could not hit infinity.

You can test this by getting some long glass like a Master Zoom and doing backfocus in a cold locker and then going outside in the sun on a hot day in LA to see if you can still hit your marks.

We never did any scientific study, but when you can hit infinity at 7am but can't at 11 and the only thing than changed was the temperature you gotta be suspicious.

I would like to know what parts of the camera are modified if we want to do a switch on the R1, and what the cost of doing so is going to be.

I'll happily call the office and ask directly, but I figured if we get an answer here it would save anyone else the trouble if they wanted one done too.

Thanks, love the camera. Keep up the strong effort.
--
Jonathan Flack
http://www.TwoFourO.com
+1 310 359-3510


>> Probably because the mount was not properly set and tightened in the first place. I've had my >camera for a year and although my assistants check back focus before every job it has not needed >any adjustment whatsoever.

I can assure you that this is not an issue with our cameras. We have a torque wrench for this that lives in the camera toolkit that travels with us.

Making sure the fasteners are all at the correct torque is in our pre-shoot checklist. I'm pretty sure ours are not just tight, they are exactly the correct torque, something I think few can say with confidence.

Can't vouch for Art but I doubt his mount is loose either, he seems to know his way around a camera.

Jonathan Flack
http://www.TwoFourO.com
+1 310 359-3510


>>If the some screws are tighter than others (if some springs are stronger than others) things can >>move in relation to each other as things heat and cool.

The screws are steel I suspect, the rest is aluminium. They have different thermal expansion properties. That throws in another dimension. Not one I think is relevant if you torque the mount down properly, but if you torque the mount when the camera is cold you should not have any issues when it heats up as things will only get tighter.

Jonathan Flack
+1 310 359-3510


Jonathan... we aim to please. The difference in thermal expansion is 15% (as has been mentioned). Element sells a stainless PV lens mount only for $850. We sell the same thing for PL mount for $850. But if you want to purchase the adjustable section AND the lens mount in stainless steel the price is $2000.

To put this in context, if an aluminium mount moves .8 microns during a quick temperature change... the stainless will "only" move .7 microns. The stainless is significantly heavier, and more expensive. Since others have shot in the same temp. change conditions, I would certainly double check how well the bolts are tightened before you purchase. If you still feel the need, we are at your service. We do request that you send your camera back to have the mount factory installed. You would be the 1st one to do this.

Jim Jannard
www.red.com
WA, NV & CA


>> Can't vouch for Art but I doubt his mount is loose either, he seems to know his way around a >>camera.

Thanks, but I don't prep them. I'm pretty good at setting them up but I leave the mechanics to my camera assistants. I might not be completely up to date on this one.

I encountered a few bugs on a recent five day RED shoot, and when I either posted about them here or called the rental house the response was always "Oh yeah, that's been going on since Build XX. -Everyone- knows about it."

Hmmm.

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Art Adams | Director of Photography
4 1 5 . 7 6 0 . 5 1 6 7

ICG, SOC, NWU


Art,

What build were you using and what were the bugs you encountered?

I'm curious because I think that a knows issues topic on RedUser would be a good start (at least on Release builds). Might be worth asking Jim to have Stuart maintain one as a sticky post.

Jonathon Flack


Jim Jannard wrote:

>> Element sells a stainless PV lens mount only for $850. We sell the same thing for PL mount for >>$850. But if you want to purchase the adjustable section AND the lens mount in stainless steel the >>price is $2000.

Jim,

I appreciate that. I am going to do a couple tests this week if I can break free of the newborn. I'll email you and Stewart the test methodology and the results. Somewhere I have an IR temp sensor and between that, a torque wrench and some spare time, I can produce a fairly scientific test on which to base the decision to buy a new mount.

The $850 price is very reasonable given the work that goes into a SS mount.

Thanks again.

Jonathon Flack


And then there is the issue of over tightening a mount, seems users think that this will keep the backfocus from drifting. The end results we believe are damaging to the system .Jim ,there is a body on the way to your guys that we suspect is such damage. It is either that or over supported or under
supported zoom lens.

As to the subject that started this thread, use of the 720p output to check BF has proven very reliable.

We checked our Eye focus against a Denz unit and we were within 2 microns, well inside the tolerance for the format .

Stacey Strode


>>"You can test this by getting some long glass like a Master Zoom and doing backfocus in a cold >>locker and then going outside in the sun on a hot day in LA to see if you can still hit your marks."

Jonathan,

did you consider front focus issues?
I have no master zoom experience but this is a known issue on 2/3" Japanese glass, especially Canon. It has been discussed on CML a couple of years ago, so if you search the archives you will get
relevant info.

It does not affect the quality of the lens, it makes life harder for the first AC though.

Best

Argyris Theos
DoP
Athens Greece
+30 6944 725315


I've been one of those customers who had sever backfocus drifts right from the start (almost two years ago) after unboxing the camera. I can remember clearly how annoying this was. I filed various service tickets and never got response (probably due to browser problems). Only the customs madness prevented me to send the camera back. But then, in a RedUser thread I opened, Steward suggested to check the bolts of the mount.

Long story short: The mount is working fine since then. Tightening the bolts is mandatory.

Hans Von Sonntaq